This project has been undertaken to examine the role of dualtropic MuLV in virus induced leukemogenesis in the mouse. Two approaches to this question are currently being taken. The first examines the role of the protein products of the recombinant env gene of dualtropic MuLV in leukemogenesis initiated by these viruses. A series of AKR dualtropic MuLV of differing leukemogenic potential are being studied to determine whether correlations exist between various parameters of structure and expression of env gene products and the in vivo activity of a particular isolate. The env gene polyprotein and gp70 are being analyzed by peptide mapping and by characterization of their associated oligosaccharide side chains; cell surface expression of env gene products is being examined in fibroblasts and in thymocytes; and the intracellular forms of the env gene polyprotein are being characterized in fibroblasts and in thymocytes. The second approach to examining the role of dualtropic MuLV in leukemogenesis in the mouse will test the hypothesis that the generation of recombinant MuLV is a necessary step in the induction of leukemia by ecotropic MuLV. Ecotropic viruses known to induce leukemia at low incidence, after long latent periods, have been injected into newborn mice of the appropriate strains. Leukemias which develop will be examined biochemically and virologically for the presence of the injected ecotropic MuLV for newly generated recombinant MuLV's.